We have entered 20 patients with a variety of metastatic solid tumors on a phase I trial of the interferon inducer poly ICLC, twice weekly IV, at doses of 1 mg/m2 or 4 mg/m2. We have not demonstrated an antitumor effect in any patient and have observed toxicity that included mild fevers, fatigue, nausea, and mild hypotension. Interferon levels have been measured in all patients studied and were consistently higher in patients treated with 4 mg/m2. Immunologic monitoring has demonstrated a consistent enhancement of monocyte-mediated cytostasis, depression of mitogen-stimulated proliferative responses in vitro, and usually decreased or in changed natural killer cell activity.